The new “Block 4” generation of guided interceptor rockets, radars and technologies for synchronizing Arrow with US systems was being installed in deployed Israeli batteries, a process that would take several weeks, the official said.

“The accuracy and the reach will be greater,” the official said of Arrow, which has been operational since 2000 and is designed to blow up incoming missiles at altitudes high enough for non-conventional warheads to disintegrate safely. “It is part of the technological race in the region,” the official, who declined to be named, told Reuters.

Long jittery about Iran’s disputed nuclear programme, the Israelis have more recently worried the Syrian insurgency could loosen Damascus’s hold on its chemical weapons and missiles.

Israel has threatened to attack preemptively in both countries, a prospect that could trigger wider war and clash with Washington’s efforts to resolve the crises diplomatically.

Iran, which denies seeking nuclear weapons, has repeatedly vowed to retaliate against any attack. “(Israel) knows that attacking Iran is an unattainable wish, unless the regime seeks to commit suicide,” Iranian Defence Minister Ahmad Vahidi was quoted as saying by the state news agency IRNA on Sunday.

The Pentagon and US firm Boeing Co are partners in Arrow, an investment that the Obama administration hopes will help stay Israel’s hand. US Secretary of Defense Leon Panetta said last week that Israeli interceptors like Arrow and Iron Dome, which shoots down short-range guerrilla rockets, were “designed to prevent wars”.

Arrow has scored a 80 percent to 90 percent success rate in field tests, system designer Uzi Rubin told Israel’s Army Radio.

“It’s always undergoing changes and improvements, as well as adaptations to new threats,” Rubin said. Iran on Saturday unveiled a new short-range missile which it said was capable of striking land and sea targets. Syria, for its part, last month went public with its chemical arsenal, saying it was intended for last-resort use against “external aggression”.

Tehran also has guerrilla allies in Lebanon and Gaza who could shell neighbouring Israel during any regional conflict. Their short-range rocket arsenals have been expanding and improving as well, the senior Israeli defence official said. Having helped underwrite Arrow, the Americans were free to draw on its technologies for their own uses, the official said.

“The policy of the (Israeli) Ministry of Defence is to provide all data to the US, for the security of the US, including on targets, interceptors, radars and command and control,” the official said.

With Congress also lavishing cash on Iron Dome, some US lawmakers have called on Israel to share that system, too.

The Israeli official said that though Iron Dome was different to Arrow as it was developed entirely by Israel, the current policy was to provide the Americans data upon request while a more permanent arrangement is negotiated.

In parallel to Arrow II, Israel is developing Arrow III, which is due to be operational in 2014 or 2015. Unlike previous generations of the interceptor, Arrow III will engage incoming missiles in space, using detachable warheads that, turning into “kamikaze” satellites, will seek out and slam into the target.

Israel is also working on a more powerful rocket interceptor than Iron Dome, known as David’s Sling or Magic Wand, which is due out next year. Meshed together and with US counterparts, the three Israeli systems would form a multi-tier shield providing several opportunities to intercept incoming missiles.